This application claims priority under 35 USC 119 of Japanese Patent Application No. 2000-76368 filed on Mar. 14, 2000, the entire disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention generally relates to a vehicle transmission that is shifted by an actuator in response to a shift lever movement, and more particularly to a transmission that realizes smooth and comfortable starting of a vehicle.
2. Description of the Related Art
A total weight and load of large trucks such as tractor-trailer greatly differs from when the tractor does not tow a trailer (or the trailer is empty and carries no load) to when the tractor tows a fully-loaded trailer. In order to maintain a satisfactory engine running condition and allow a driver to drive a vehicle comfortably in any situations, a large truck has a considerably greater number of gear positions than a small truck (e.g., pick-up truck). For example, the large truck is equipped with a four-gear main gear assembly, a two-gear splitter gear assembly of relatively small gear ratio in front of the main gear assembly, and a two-gear range gear assembly of relatively large gear ratio behind the main gear assembly. The combination of the splitter gear assembly, main gear assembly and range gear assembly provides sixteen gear positions as a whole. By employing such large-number-gear transmission, a driver can select a suitable gear so that an appropriate engine condition is obtained across a wide range of vehicle speed. Further, the driver can accelerate and decelerate the vehicle smoothly.
Gear position change is effected by an actuator under the control of an associated controller (computer). However, initiation of the gear position change is effected by either automatically under the control of the computer or manually. The driver can momentarily tilt a shift lever to the front and back from a D position or range (=H position), which is a stable driving gear position. In the manual shift mode, if the driver moves the shift lever forward from the H position, the computer recognizes that the driver wants to shift up the transmission, and if the driver moves the shift lever backward, the computer assumes that the driver intends to shift down the transmission. Subsequently, the computer shifts up or down the transmission from a current gear position. By repeating this shift up (or down) operation, the transmission gear position is gradually raised (or lowered). In the automatic shift mode, the driver does not move the shift lever; instead, the shift lever remains in the D position. The computer selects a most appropriate gear position based on an engine running condition and/or vehicle speed.
Although the transmission has sixteen gears, all the gears from the first to sixteenth are not used during driving. Some of the gears may be frequently utilized depending upon vehicle load condition, driver""s intention, etc. For instance, when a large truck with a trailer starts moving, a very low gear position such as first or second gear is generally selected if the trailer carries a relatively heavy load. However, if the load is not so heavy, a relatively high gear position such as fourth, fifth or sixth gear may be selected. In the latter case, the tractor-trailer can smoothly start and accelerate with the relatively high gear, and the driver can experience comfortable starting. Further, since clutch disengagement and engagement take place less frequently as compared with the former case, clutch wear is reduced and its life is elongated. If the tractor does not tow the trailer, a still higher gear such as ninth gear may be selected to experience comfortable starting. The lowest gear (first or second gear) may be selected in a particular situation (when circumstances demand), e.g., when the vehicle starts on an uphill, when an engine torque should be raised because of low atmospheric pressure in mountains, and when the driver should operate the vehicle delicately at a low speed (to park in a garage).
In order to start the large truck having sixteen gear positions smoothly, a gear for starting should be selected appropriately based on a vehicle load, road condition, driver""s intention, atmospheric condition, etc. However, the shift lever only allows shifting up and down so that the first gear is always selected in every initial setting and the shift lever operation must be repeated until a desired start gear is reached. Thus, the driver is required to tilt the shift lever repeatedly every time the driver wants to start the vehicle from a stop condition. This is troublesome and a certain period is needed until the vehicle starts, thereby degrading driving comfort.
To solve the above described problem, Japanese Patent Application, Laid Open Publication No. 7-63252 entitled xe2x80x9cAutomatic Transmission of Vehiclexe2x80x9d discloses an arrangement that determines starting of a vehicle from vehicle speed and memorizes a transmission gear at that vehicle speed as a start gear for a next starting of the vehicle. When the vehicle is started next time, the memorized gear position is immediately selected whereby the driver does not have to shift up the transmission to reach a desired start gear. According to this technique, rising up of the vehicle speed from zero is a trigger condition to memorize the gear position so that the current start gear position is always memorized for the next start up every time the vehicle is started. However, driving circumstances are not always the same. For example, an unusual gear should be selected if the vehicle starts on an uphill. Such gear position is memorized for the next start according the conventional technique. If the vehicle starts on a flat road next time, the previous start gear position is not appropriate for the start of this time. This makes the driver uncomfortable.
Further, a suitable start gear position for the tractor is significantly different from when the tractor tows the trailer to when the tractor does not the trailer. When the tractor starts without the trailer and stops and then the tractor is restarted with the trailer, the start gear position suited for the no trailer condition is applied to the tractor with the trailer. This makes the start awkward.
One of the objects of the present invention is to provide a multi-gear transmission that can solve the above problems.
According to one aspect of the present invention, there is provided a vehicle transmission arrangement including an actuator for shifting a transmission, a controller for causing the actuator to shift the transmission based on movement of a shift lever, and a learning unit for memorizing a gear position of when a vehicle is stopped, a brake pedal is stamped, an accelerator pedal is not stamped, and a certain transmission gear is selected, as a start gear, and for selecting the memorized start gear for subsequent starting of the vehicle.
The learning unit may memorize the gear position if the vehicle is stopped over a predetermined period (e.g., about 1.5 seconds). The learning unit may separately memorize the gear position of when the vehicle tows another vehicle (e.g., sixth gear) and the gear position of when the vehicle does not tow another vehicle (e.g., ninth gear). The controller may not cause the actuator to shift the transmission if the gear position instructed by the shift lever movement for starting is higher than a predetermined gear position. Alternatively the controller may cause the actuator to shift the transmission to a predetermined gear if the gear position instructed by the shift lever movement for starting is higher than the predetermined gear position. The arrangement may further include a detector for determining whether the vehicle tows another vehicle or not.